Study On The Inelastic Displacement Estimation Of Aseismatic Structures

Nowadays, most of codes for seismic design of building all over the world are based on strength and preferable ductility through details of seismic design. Thus, it's important to control the deformation of buildings in their inelastic stage. Besides, several earthquakes occurred in developed countries in the last decade of the 20th century (eg. Northridge earthquake, Kobe earthquake et al.) made researchers recognized that it was not a perfect theory of seismic design to avoid collapse of structures. So the theory of displacement based seismic design in which displacement is the mainly controlling parameter became the hotspot in the field of earthquake engineering recently. It can be seen through above discussions that whether in the theory of strength-based seismic design or the theory of displacement-based seismic design, it's significant to provide a simple and effective method to estimate displacement.The displacement ratio method is investigated systemically in this paper. The displacement ratio method is also called displacement ratio spectra method. The maximum inelastic displacement of structures can be estimated from the maximum elastic displacement with the method. On the basis of 476 strong ground motions collected all over the world, mean inelastic displacement ratio spectra are obtained. And a new experimental expression of inelastic displacement ratio spectra from non-linear regression is developed.The influence of restoring force models on inelastic displacement ratio spectra is studied for two aspects, stiffness degrading and yield stiffness. With Clough restoring force model, the effect of stiffness degrading is studied and the effect of yield stiffness is studied by changing the second stiffness ratio of bilinear restoring force model.The P-Δeffect on the inelastic displacement ratio spectra is studied by calculating the displacement ratios of SDOF systems for different degree of P-Δeffect. Then, the strong ground motion records are classified according to 90% energy duration of strong ground motion, so as to investigate the influence of duration of strong ground motion to the inelastic displacement ratio spectra considering P-Δeffect.